Unlocked 6620, Cingular GPRS web problems

Hi, I'm wondering if anyone else has had strange data connection problems with a Cingular 6620 or 6600 after unlocking and using Cingular data service? It was working fine before.

When I try to load a web page, it starts to load the first part of it (see the top title), then kicks out completely, regardless of web browser, etc. The MMS and email still work fine! I've tried the following:

1) Checked the 'Media Net' settings against what is recommended in multiple places on the web. I also got the config SMS for the Web settings sent to me from the Nokia website, for Cingular, but it still doesn't work. The Nokia config SMS created a connection called 'Cingular Express', and it's settings are exactly the same as 'Media Net'.
2) My wife's 6230 is also unlocked and has no problems accessing the web, however, it uses the 'isp.cingular' settings versus the 'wap.cingular' settings on the 6620. I also tried swapping SIM cards, but the problem stays with the phone.
3) I tried soft reseting the device as well, using a command given in another forum. I didn't try the hard reset and format (and don't want to).

I've seen rumblings around the web about this, but nothing definitive. People claim that their phone works fine for voice calls after unlocking, but has data problems. Has anybody heard of anything like this? Can Cingular's data service tell whether your phone is SIM unlocked or not?

Thanks,
Dan